The attributes available for customweps.txt are Here (at the bottom, ignore min/max values).
The first key is the number above the attribute you want, and the second is the value.
Make sure the attribute count is correct, otherwise the server will most likely crash, I do not advise going over 7-11, YMMV.

At the moment, yes. In the next version I plan to add wildcarding and admin flag checks, bear in mind though that you can only currently edit the attributes of the base weapons, not the unlockables. The quality and level are fine however.
Edit: Turns out you can edit the unlockable's attributes, bear in mind that it completely overwrites existing ones though.